The present invention relates to a method of recovering methyl chloride and methylene chloride. More particularly, the invention relates to the recovery of methyl chloride and methylene chloride from gaseous mixtures containing significant amounts of relatively noncondensable gases produced in the chlorination of methane. In its preferred form, the invention relates to the recovery of methyl chloride and methylene chloride from cooled reactor effluents extant in that type of methane chlorination process described as "oxychlorination". The invention also comprises a novel process for the oxychlorination of methane which features improved and economical recovery of methyl chloride and methylene chloride.
Although the chlorination of methane with Cl.sub.2 or HCl is known in the art, frequently there are serious operational problems generally associated with this type of reaction. For example, considerable difficulty may be experienced in oxychlorination processes in the recovery of the chlorinated methanes issuing from the reaction. One reason for this problem is the fact that the chlorinated methane products are likely to be diluted in great or significant quantities of inert or relatively noncondensable gases such as nitrogen, carbon monoxide, HCl, carbon dioxide, and other similar gases. In order to recover the products satisfactorily from such a process, it would be necessary to process great quantities of gas and efficiently recover the chlorinated methane content thereof. This may be accomplished by a "condensation" step; or series of steps, in which the gaseous chlorination or oxychlorination reactor effluent is cooled, for example, by contacting the effluent with a cooling medium, such as chilled water or other cooling liquids, followed by separation of the liquid and gaseous phases.
While condensation of large volumes of chlorinated methanes in such a fashion is technologically feasible, the procedure is complicated due to the low boiling characteristics of methyl chloride and methylene chloride. A typical oxychlorination reactor effluent, after the "condensation" or cooling step or steps, may contain roughly, by weight, based on the total weight of the effluent, from about one to about twenty percent methyl chloride, from trace amounts (0.01 percent or less) to about 10 percent methylene chloride, and from negligible or trace amounts up to five percent of chloroform and carbon tetrachloride combined. In order to remove the methyl chloride and methylene chloride from the effluent, after the aforementioned "condensation" step or steps, expensive additional cooling would be necessary, thus rendering the complete recovery of these low-boiling materials uneconomical. In the case of oxychlorination processes, the relatively high freezing point of CO.sub.2 poses additional problems.